Electrode structure of light emitting device

ABSTRACT

A light-emitting device comprises a first semiconductor layer; an active layer on the first semiconductor layer; a second semiconductor layer on the active layer; and an electrode structure on the second semiconductor layer, wherein the electrode structure comprises an adhesion layer on the second semiconductor layer, a conductive layer on the adhesion layer, and a bonding layer on the conductive layer, and wherein the electrode structure comprises a center region and an edge region, a thickness of each layer of the edge region of the electrode structure is smaller than that of the center region.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 15/049,917, filed on Feb. 22, 2016, which is acontinuation application of U.S. patent application Ser. No. 13/854,212,filed on Apr. 1, 2013, now issued, which claims the right of prioritybased on U.S. Provisional Application No. 61/721,737, filed on Nov. 2,2012 and the contents of which are hereby incorporated by references intheir entireties.

TECHNICAL FIELD

The present application relates to a light-emitting device with anexcellent electrode structure to improve the reliability thereof.

DESCRIPTION OF BACKGROUND ART

As the light-emitting efficiency is increased and the cost ofmanufacturing is decreased, the dream for solid lighting device toreplace the traditional lighting device may come true in recent years.Currently, the internal light-emitting efficiency of the light-emittingdiode is about 50% to 80%, but a part of the light may be absorbed bythe electrode or the light-emitting layer so the total light-emittingefficiency is degraded. Therefore, the mirror layer under the electrodehas been provided to solve the problem. When the route of the lightextracted from the light-emitting layer is blocked by the electrode, themirror can reflect but not absorbs the light. On the other hand, theelectrode has a bonding pad for wire bonding, and the bonding pad isusually made of gold (Au). Since gold (Au) is very expensive, the costof the electrode is increased.

SUMMARY OF THE DISCLOSURE

A light-emitting device, comprising: a substrate; a semiconductorstacking layer comprising a first type semiconductor layer on thesubstrate, an active layer on the first semiconductor layer, and asecond semiconductor layer on the active layer; and an electrodestructure on the second semiconductor layer, wherein the electrodestructure comprises a bonding layer, a conductive layer, and a firstbarrier layer between the bonding layer and the conductive layer;wherein the conductive layer has higher standard oxidation potentialthan that of the bonding layer.

A light-emitting device comprises a first semiconductor layer; an activelayer on the first semiconductor layer; a second semiconductor layer onthe active layer; and an electrode structure on the second semiconductorlayer, wherein the electrode structure comprises an adhesion layer onthe second semiconductor layer, a conductive layer on the adhesionlayer, and a bonding layer on the conductive layer, wherein the bondinglayer comprises a first metal, the conductive layer comprises a secondmetal, the second metal has higher standard oxidation potential than thefirst metal, and wherein a total thickness of the conductive layer andthe bonding layer is 0.75˜0.95 times a thickness of the electrodestructure.

A light-emitting device comprises a first semiconductor layer; an activelayer on the first semiconductor layer; a second semiconductor layer onthe active layer; and an electrode structure on the second semiconductorlayer, wherein the electrode structure comprises an adhesion layer onthe second semiconductor layer, a conductive layer on the adhesionlayer, and a bonding layer on the conductive layer, and wherein theelectrode structure comprises a center region and an edge region, athickness of each layer of the edge region of the electrode structure issmaller than that of the center region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a light-emitting device in accordance with thefirst embodiment of the present application;

FIG. 2 shows the detailed structure of an electrode structure inaccordance with the first embodiment of the present application;

FIGS. 3A and 3B show the detailed structure of an electrode structure inaccordance with the second embodiment of the present application;

FIG. 4 shows the detailed structure of an electrode structure inaccordance with the third embodiment of the present application.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary embodiments of the present application will be described indetail with reference to the accompanying drawings hereafter. Thefollowing embodiments are given by way of illustration to help thoseskilled in the art fully understand the spirit of the presentapplication. Hence, it should be noted that the present application isnot limited to the embodiments herein and can be realized by variousforms. Further, the drawings are not precise scale and components may beexaggerated in view of width, height, length, etc. Herein, the similaror identical reference numerals will denote the similar or identicalcomponents throughout the drawings.

FIG. 1A shows a light-emitting device 1 comprising a substrate 10, afirst semiconductor layer 11 having a first polarity, such as an n-typeGaN layer, on the substrate 10, an active layer 12 having a structure,such as InGaN-based multiple-quantum-well (MQW) structure, on the firstsemiconductor layer 11, a second semiconductor layer 13 having a secondpolarity, such as a p-type GaN layer, on the active layer 12, atransparent conductive oxide layer 14 comprising a first metal material,such as indium tin oxide (ITO), on the second semiconductor layer 13, atop surface S2 of the first semiconductor layer 11 revealed from theactive layer 12 and the second semiconductor layer 13, a first electrodestructure 61 on the top surface S2, and a second electrode structure 62on a top surface S1 of the transparent conductive oxide layer 14.

The substrate 10 can be an insulating substrate, such as sapphire. Inanother embodiment, a vertical-type light-emitting device 2 is alsodisclosed in FIG. 1B by arranging a third electrode structure 63 and thesecond electrode structure 62 on opposite sides of a conductivesubstrate 21. The conductive substrate 21 comprises a conductivematerial, such as metal, e.g. Cu, Al, In, Sn, Zn, W or the combinationthereof, or semiconductor, e.g. Si, SiC, GaN, GaAs, etc.

The material of the first semiconductor layer 11, the active layer 12,and the second semiconductor layer 13 comprise group III-V compoundsemiconductor, such as gallium phosphide (GaP), gallium arsenide (GaAs),or gallium nitride (GaN). The first semiconductor layer 11, the secondsemiconductor layer 13, or the active layer 12 may be formed by a knownepitaxy method such as metallic-organic chemical vapor deposition(MOCVD) method, a molecular beam epitaxy (MBE) method, or a hydridevapor phase epitaxy (HVPE) method.

The material of the transparent conductive oxide layer 14 comprisestransparent conductive oxide material, such as indium tin oxide (ITO),cadmium tin oxide (CTO), antimony tin oxide, indium zinc oxide, zincaluminum oxide, zinc oxide, and zinc tin oxide. The transparentconductive oxide layer 14 has a predetermined thickness such as smallerthan 3000 angstroms and if formed by a evaporation deposition methodunder chamber conditions of around room temperature, N2 ambientenvironment, and a pressure between 1×10⁻⁴ Torr and 1×10⁻² Torr, orpreferably around 5×10⁻³ Torr.

First Embodiment

FIG. 2 shows an electrode structure 7 which details the first electrodestructure 61, the second electrode structure 62, and the third electrodestructure 63 in accordance with the first embodiment. The electrodestructure 7 comprises a bonding layer 71 for wire bonding, a conductivelayer 76 under the bonding layer 71, a mirror layer 72 under theconductive layer 76 for reflecting the light emitted from the activelayer 12, an adhesion layer 73 for increasing the adhesion between themirror layer 72 and the transparent conductive structure 14 or the firstsemiconductor layer 11, a second barrier layer 74 between the conductivelayer 76 and the mirror layer 72 for separating the conductive layer 76from directly contacting the mirror layer 72, and a first barrier layer75 between the bonding layer 71 and the conductive layer 76 forseparating the conductive layer 76 from directly contacting the bondinglayer 71.

The bonding layer 71 comprises a first metal, e.g. Au. The thickness ofthe bonding layer 71 is between 1000 Å and 42000 Å, and preferably isbetween 5000 Å and 10000 Å. The conductive layer 76 comprises a secondmetal different from the first metal, e.g. Al, Ag, or Cu. The electricalconductivity of the second metal is 0.1˜10 times the electricalconductivity of the first metal. The first metal is more chemicallystable than the second metal, or the second metal has higher standardoxidation potential than the first metal. The thickness of theconductive layer 76 is 0.1˜10 times the thickness of the bonding layer71. The thickness of the conductive layer 76 depends on the amount ofoperating current flowing through the electrode structure 7. If theelectrical conductivity of the bonding layer 71 is smaller than that ofthe conductive layer 76 under a low to moderate driving current injectedinto the electrode structure 7, e.g. 120 mA˜300 mA, a first ratio of thethickness of the conductive layer 76 to the total thickness of theelectrode structure 7 is between 0.3 and 0.5. The total thickness of theconductive layer 76 and the bonding layer 71 is about 0.4˜0.7 times thetotal thickness of the electrode structure 7. If the electricalconductivity of the bonding layer 71 is smaller than that of theconductive layer 76 under a high driving current injected into theelectrode structure 7, e.g. 350 mA˜1000 mA, a second ratio of thethickness of the conductive layer 76 to the total thickness of theelectrode structure 7, which is greater than the first ratio, is between0.5 and 0.8. The total thickness of the conductive layer 76 and thebonding layer 71 is about 0.6˜0.9 times the total thickness of theelectrode structure 7. If the electrical conductivity of the bondinglayer 71 is greater than that of the conductive layer 76, when a low tomoderate driving current injects into the electrode structure 7, e.g.120 mA˜300 mA, a third ratio of the thickness of the conductive layer 76to the total thickness of the electrode structure 7 is between 0.4 and0.7, or the total thickness of the conductive layer 76 and the bondinglayer 71 is about 0.5˜0.8 times the total thickness of the electrodestructure 7. If the electrical conductivity of the bonding layer 71 isgreater than that of the conductive layer 76 under a high drivingcurrent injected into the electrode structure 7, e.g. 350 mA˜1000 mA, afourth ratio of the thickness of the conductive layer 76 to the totalthickness of the electrode structure 7, which is greater than the thirdratio, is between 0.55 and 0.85. The total thickness of the conductivelayer 76 and the bonding layer 71 is about 0.75˜0.95 times the totalthickness of the electrode structure 7. The mirror layer 72 comprisesmetal having a reflectivity greater than 80% to the light emitted fromactive layer 12, e.g. Al or Ag. The thickness of the mirror layer 72 ispreferably between 500 Å and 5000 Å.

The second barrier layer 74 serves to separate the mirror layer 72 fromthe conductive layer 76 to prevent the conductive layer 76 frominter-diffusing with the mirror layer 72 at the in-between interface andform low contact resistance and good adhesion between the mirror layer72 and the bonding layer 71. The second barrier layer 74 comprises athird metal layer and a fourth metal layer stacked on the third metallayer, wherein the fourth metal layer comprises a material differentfrom the third metal layer. In another embodiment, the second barrierlayer 74 comprises a plurality of the third metal layers and a pluralityof fourth metal layers alternately stacked, e.g. Ti/Pt/Ti/Pt orTi/Pt/Ti/Pt/Ti/Pt. The third metal layer is preferred about one to threetimes thicker than the fourth metal layer. The thickness of the thirdmetal layer is between 500 Å and 1500 Å and the thickness of the fourthmetal layer is between 250 Å and 750 Å. The third metal layer and thefourth metal layer each comprises a material selected from the groupconsisting of Cr, Pt, Ti, TiW, W, and Zn. Therefore, the second barrierlayer 74 comprises at least two materials selected from the groupconsisting of Cr/Pt, Cr/Ti, Cr/TW, Cr/W, Cr/Zn, Ti/Pt, Ti/W, Ti/TiW,Ti/W, Ti/Zn, Pt/TiW, Pt/W, Pt/Zn, TiW/W, TiW/Zn, and W/Zn. The firstbarrier layer 75 serves to separate the bonding layer 71 from theconductive layer 76 to prevent the conductive layer 76 frominter-diffusing with the bonding layer 71 at the in-between interfaceand form low contact resistance and good adhesion between the bondinglayer 71 and the conductive layer 76. The first barrier layer 75comprises a first metal layer and a second metal layer stacked on thefirst metal layer, wherein the first metal layer comprises a materialdifferent from the second metal layer. In another embodiment, the firstbarrier layer 75 comprises a plurality of the first metal layers and aplurality of second metal layers alternately stacked, e.g. Ti/Pt/Ti/Ptor Ti/Pt/Ti/Pt/Ti/Pt. The first metal layer is preferred about one tothree times thicker than the second metal layer. The thickness of thefirst metal layer is between 500 Å and 1500 Å and the thickness of thesecond metal layer is between 250 Å and 750 Å. The first metal layer andthe second metal layer each comprises a material selected from the groupconsisting of Cr, Pt, Ti, TiW, W, and Zn. Therefore the first barrierlayer 75 comprises at least two materials selected from the groupconsisting of Cr/Pt, Cr/Ti, Cr/TW, Cr/W, Cr/Zn, Ti/Pt, Ti/W, Ti/TiW,Ti/W, Ti/Zn, Pt/TiW, Pt/W, Pt/Zn, TiW/W, TiW/Zn, and W/Zn. The adhesionlayer 73 is used to increase adhesion between the mirror layer 72 andthe transparent conductive structure 14 or the first semiconductor layer11. The adhesion layer 73 preferably comprises Cr or Rh. The thicknessof the adhesion layer 73 is preferably between 5 Å and 50 Å such thatthe adhesion layer 73 is thin enough to be pervious to the light emittedfrom the active layer 12.

For each of the mirror layer 72, the second barrier layer 74, theconductive layer 76, the first barrier layer 75, and the bonding layer71, the thickness of each of these layers in an edge region A or B issmaller than that in a center region C. The shape of the electrodestructure 7 is approximately a trapezoid, or preferred a non-symmetricaltrapezoid with two opposite sides having different slopes.

Second Embodiment

FIG. 3A shows an electrode structure 8 which details the first electrodestructure 61, the second electrode structure 62, and the third electrodestructure 63 in accordance with the second embodiment. FIG. 3B shows thescanning electron microscope (SEM) figure of the detailed structure ofthe electrode structure 8. The difference between the electrodestructure 8 of FIG. 3A and the electrode structure 7 of FIG. 2 is thatthe conductive layer 76 of the electrode structure 7 is divided into twoparts, i.e. a first conductive layer 761 and a second conductive layer762, and a third barrier layer 77 is between the first conductive layer761 and the second conductive layer 762 to reduce out-diffusing of thefirst conductive layer 761 and the second conductive layer 762 to thebonding layer 71 or the mirror layer 72 caused by electron migrationeffect when a high driving current injected into the electrode structure8. The first conductive layer 761 and the second conductive layer 762comprise substantially the same material, and the thickness of the firstconductive layer 761 is about equal to or of the same order as that ofthe second conductive layer 762. The third barrier layer 77 comprises amaterial different from the material of the first conductive layer 761or the second conductive layer 762. The third barrier layer 77 comprisesa single metal layer selected from the group consisting of Cr, Pt, Ti,TiW, W, and Zn. The thickness of the single metal layer is between 500 Åand 1500 Å.

For each of the mirror layer 72, the second barrier layer 74, the firstconductive layer 761, the third barrier layer 77, the second conductivelayer 762, the first barrier layer 75, and the bonding layer 71, thethickness of each of these layers in an edge region A or B is smallerthan that in a center region C. The shape of the electrode structure 8is approximately a trapezoid, or preferred a non-symmetrical trapezoidwith two opposite sides having different slopes.

Third Embodiment

FIG. 4 shows an electrode structure 9 which details the first electrodestructure 61, the second electrode structure 62, and the third electrodestructure 63 in accordance with the third embodiment. The differencebetween the electrode structure 9 of FIG. 4 and the electrode structure7 of FIG. 2 is that the conductive layer 76 of the electrode structure 7is divided into three parts, i.e. the first conductive layer 761, thesecond conductive layer 762 and a third conductive layer 763, and thesecond conductive layer 762 and the third conductive layer 763 isseparated by a fourth barrier layer 78. The thicknesses of the firstconductive layer 761, the second conductive layer 762 and the thirdconductive layer 763 are about equal, or of the same order. The fourthbarrier layer 78 comprises the same material as the third barrier layer77.

For each of the mirror layer 72, the second barrier layer 74, the firstconductive layer 761, the third barrier layer 77, the second conductivelayer 762, the fourth barrier layer 78, the third conductive layer 763,the first barrier layer 75, and the bonding layer 71, the thickness ofeach of these layers in an edge region A or B is smaller than that in acenter region C, and each of these layers in the edge region A or B isbended downward toward the active layer 12. The shape of the electrodestructure 9 is approximately a symmetrical trapezoid, or preferred anon-symmetrical trapezoid with two opposite sides having differentslopes.

The foregoing description of preferred and other embodiments in thepresent disclosure is not intended to limit or restrict the scope orapplicability of the inventive concepts conceived by the Applicant. Inexchange for disclosing the inventive concepts contained herein, theApplicant desires all patent rights afforded by the appended claims.Therefore, it is intended that the appended claims include allmodifications and alterations to the full extent that they come withinthe scope of the following claims or the equivalents thereof.

What is claimed is:
 1. A light-emitting device, comprising: a firstsemiconductor layer; an active layer on the first semiconductor layer; asecond semiconductor layer on the active layer; and an electrodestructure on the second semiconductor layer, wherein the electrodestructure comprises an adhesion layer on the second semiconductor layer,a conductive layer on the adhesion layer, and a bonding layer on theconductive layer, and a barrier layer between the adhesion layer and theconductive layer, wherein the barrier layer comprises a third metallayer and a fourth metal layer, the third metal layer and the fourthmetal layer each comprises a material selected from a group consistingof Cr, Pt, Ti, TiW, W, and Zn, wherein the bonding layer comprises afirst metal, the conductive layer comprises a second metal, the secondmetal has higher standard oxidation potential than the first metal, andwherein a thickness of the conductive layer is 0.1˜10 times a thicknessof the bonding layer or a total thickness of the conductive layer andthe bonding layer is 0.75˜0.95 times a thickness of the electrodestructure.
 2. A light-emitting device according to claim 1, wherein theadhesion layer comprises Cr or Rh.
 3. A light-emitting device accordingto claim 1, wherein the adhesion layer comprises a thickness between 5 Åand 50 Å.
 4. A light-emitting device according to claim 1, furthercomprising a mirror layer between the adhesion layer and the conductivelayer, wherein the mirror layer comprises Al or Ag.
 5. A light-emittingdevice according to claim 4, wherein the mirror layer comprises athickness between 500 Å and 5000 Å.
 6. A light-emitting device accordingto claim 1, wherein the first metal comprises Au, the second metalcomprises Al, Ag, or Cu.
 7. A light-emitting device according to claim1, wherein the third metal layer is one to three times thicker than thefourth metal layer.
 8. A light-emitting device according to claim 1,wherein the electrode structure comprises a center region and an edgeregion, a thickness of each layer of the edge region of the electrodestructure is smaller than that in the center region.
 9. A light-emittingdevice, comprising: a first semiconductor layer; an active layer on thefirst semiconductor layer; a second semiconductor layer on the activelayer; and an electrode structure on the second semiconductor layer,wherein the electrode structure comprises an adhesion layer on thesecond semiconductor layer, a conductive layer on the adhesion layer, abonding layer on the conductive layer, and a barrier layer between thebonding layer and the conductive layer, wherein the barrier layercomprises a third metal layer and a fourth metal layer, the third metallayer and the fourth metal layer each comprises a material selected froma group consisting of Cr, Pt, Ti, TiW, W, and Zn, and wherein theelectrode structure comprises a center region and an edge region, athickness of the barrier layer at the edge region of the electrodestructure is smaller than that at the center region.
 10. Alight-emitting device according to claim 9, wherein the bonding layercomprises a first metal, the conductive layer comprises a second metal,and the second metal has higher standard oxidation potential than thefirst metal.
 11. A light-emitting device according to claim 9, whereinthe adhesion layer comprises Cr or Rh.
 12. A light-emitting deviceaccording to claim 9, wherein the adhesion layer comprises a thicknessbetween 5 Å and 50 Å.
 13. A light-emitting device according to claim 9,further comprising a mirror layer between the adhesion layer and theconductive layer, wherein the mirror layer comprises Al or Ag.
 14. Alight-emitting device according to claim 13, wherein the mirror layercomprises a thickness between 500 Å and 5000 Å.
 15. A light-emittingdevice according to claim 10, wherein the first metal comprises Au, thesecond metal comprises Al, Ag, or Cu.
 16. A light-emitting device,comprising: a first semiconductor layer; an active layer on the firstsemiconductor layer; a second semiconductor layer on the active layer;and an electrode structure on the second semiconductor layer, whereinthe electrode structure comprises an adhesion layer on the secondsemiconductor layer, a conductive layer on the adhesion layer, a bondinglayer on the conductive layer, and a barrier layer between the bondinglayer and the conductive layer, wherein the barrier comprises a thirdmetal layer and a fourth metal layer, wherein the third metal layer isone to three times thicker than the fourth metal layer, and wherein theelectrode structure comprises a center region and an edge region, athickness of the barrier layer at the edge region of the electrodestructure is smaller than that at the center region.
 17. Alight-emitting device according to claim 16, wherein the first metalcomprises Au, the second metal comprises Al, Ag, or Cu.
 18. Alight-emitting device according to claim 16, wherein the adhesion layercomprises Cr or Rh.
 19. A light-emitting device according to claim 16,further comprising a mirror layer between the adhesion layer and theconductive layer, wherein the mirror layer comprises Al or Ag.